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Causes and effects of 20th century wars

This topic focuses on the causes, practice and effects of war in the 20th century. The topic explores the causes of wars, as well as the way in which warfare was conducted, including types of war, the use of technology, and the impact these factors had upon the outcome.


Examination questions for this topic will require students to make reference to specific 20th-century wars in their responses, and some examination questions will require discussion of wars from more than one region of the world. 

Causes of war

  • Economic, ideological, political, territorial and other causes

  • Short- and long-term causes

Practices of war and their impact on the outcome

  • Types of war: civil wars; wars between states; guerrilla wars

  • Technological developments; theatres of war—air, land and sea

  • The extent of the mobilization of human and economic resources

  • The influence and/or involvement of foreign powers

Effects of war

  • The successes and failures of peacemaking

  • Territorial changes

  • Political repercussions

  • Economic, social and demographic impact; changes in the role and status of women - Glossary for SCW figures, events, organisations

What is War?  What differentiates 20thC war from its predecessors?

ib access cpe war.jpg

Arriving at an answer to the first question is relatively easy on the surface.  However, the increasing complexity of the modern world has seen a parallel increase in what constitutes war and how it is fought.

The 20thC, especially in the first 50 years, saw an explosion in wars fought around the world with increasingly advanced tools used, but not necessarily always by the winning side.  Wars were fought over modern motives such as ideology and resources, as opposed to previous centuries' concerns such as religion.  That isn't to say that these weren't still important, especially in the first such war we look at, but increasingly war was becoming a political and economic tool rather than one based on faith.

Using the e-book version of your text on the left, read the first section on what you will study and note down the different types of wars that this unit features...


The Spanish Civil War - Andrew Forrest (Routledge 2000 - online version) 

Causes of the Spanish Civil War - why was there a conflict at all...?

Landmark British TV series - Spanish Civil War - episode 1 (Granada TV)

The war was an outcome of the polarisation of Spanish life and politics that had developed over the previous century, fragmenting society along multiple fissures.  WWI was followed by a shortlived + unsuccessful mlitary dictatorship under Primo de Rivera which found itself ousted and replaced in 1931 by a democratic 2nd Republic.


On one side, the Nationalist, were mostly Roman Catholic establishment figures & supporters, important elements of the military, most landowners, and many businessmen. On the other side, the Republican, were urban workers, most agricultural labourers, and many of the educated middle class.


Politically, their differences often found extreme and vehement expression in parties such as the Fascist-oriented Falange and the militant anarchists. Between these extremes were other groups covering the political spectrum from monarchism and conservatism through liberalism to socialism, including a small communist movement divided among followers of the Soviet leader Joseph Stalin and his arch-rival, Leon Trotsky.


In 1934 there was widespread labour conflict and a bloody uprising by miners in Asturias that was suppressed by troops led by General Francisco Franco. A succession of governmental crises culminated in the elections of February 16, 1936, which brought to power a Popular Front government supported by most of the parties of the left and opposed by the parties of the right and what remained of the centre.  A well-planned military uprising began on July 17, 1936, in garrison towns throughout Spain....

00:00 / 41:17


Causes of the Spanish Civil War

Paul Prestons's 'The Concise History of the SCW' -  opening chapter via PDF icon - wider reading

Access scanned text by clicking on flag to the left to work through the chapter, completing the activities:

  1. 74-78 - LT causes of CW timeline 

  2. 86 - Political Parties in Spain - copy spectrum

  3. 79 - Problems facing Govts 31-36 - overview

  4. 79-82 - LW reforms 31-33; limitations; opp mindmap

  5. 83-84 - RW reaction 33-36; Asturias, collapse timeline

  6. 84-85 - Popular Front Feb-July 36 reforms v opp chart

  7. 85-86 - 36 Military uprising - overview

Next, listen to the BBC In Our Time podcast on the left, up to 19.00, and summarise what the debating historians believe are the causes of the SCW...

BBC Radio 4 - In Our Time (August 4 2018) - Melvyn Bragg and guests discuss the Spanish Civil War which was a defining war of the twentieth century. It was a brutal conflict that polarised Spain, pitting the Left against the Right, the anti-clericals against the Church, the unions against the landed classes and the Republicans against the Monarchists. It was a bloody war which saw, in the space of just three years, the murder and execution of 350,000 people. It was also a conflict which soon became internationalised, becoming a battleground for the forces of Fascism and Communism as Europe itself geared up for war. 

  • What were the roots of the Spanish Civil War?

  • To what extent did Franco prosecute the war as a religious crusade?

  • How did Franco institutionalise his victory after the war?

  • And has Spain fully come to terms with its past?


With Paul Preston, Principe de Asturias Professor of Contemporary Spanish History at the London School of Economics; Helen Graham, Professor of Spanish History at Royal Holloway, University of London; Dr Mary Vincent, Senior Lecturer in the Department of History at Sheffield University.

download 2ndrepscw.png that you have researched the events leading up to the outbreak of hostilities in 1936, we need to start establishing a framework for these complex and numerous causes.  In the googledoc on the left, note down the key events/policies of each stage of the 2nd Republic and then discuss how each stage contributed to war breaking out.... 

Causes of the Spanish Civil War hexagons card sort

- Using the student list of causes of the SCW, hexagon sheets are printed off.  These are sorted into categories, or themes, which help explain the outbreak of war. 

- Once these categories have been identified, they need to be organised by linking the causes together.  Stronger causes will have more links and so be identified.

- With the categories sorted, look at how your themes interconnect and which themes are fundamental to explaining the war and why....

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So how do we assess the causes of the Spanish Civil war?  There are surprisingly (!) a wide variety of interpretations which are fiercely contested between eminent academics.  Two contrasting views are held by the two historians pictured l+r

Stanley Payne is an American historian whose bio can be accessed by clicking his photo on the left, whilst Paul Preston, who you've heard in the podcast, can be seen on the right with his details also available by clicking on said photo.

Once you are familiar with who they are, read (1) an interview with Payne, below left; and then (2) a review of Payne's work on General Franco, below right, in which the reviewer (himself a respected academic) contrasts Payne's + Preston's ideas...

payne scw.jpg

Having read about both historians, and researched their contrasting views on the causes of the Spanish Civil War, your job as historians is to assess their theories.

How do we do this? Using the OPCVL skills used in Paper 1 + outlined below, each historian's origins and purpose need to be considered and values and limitations given to each based on their ideas, or their content.

In groups, construct an OPCVL table and using the podcast and interview as content, evaluate the values and limitations of each historian and their interpretation of the causes of the Spanish Civil war.  Which one do you agree with?

payne scw ii.jpg

Course of the Spanish Civil War - conventional, guerrilla, total?

The war itself was extremely horrific. There was a considerable amount of interference from other countries mainly because the war was a fight between the left and right factions. The fascist governments of Germany and Italy gave their support to the Nationalists under General Franco. Up until the outbreak of the war Franco had amassed his troops in Morocco. They were unable to cross back into Spain until Hitler and Mussolini provided airlifts. This began the forward push of Franco and ultimately led to his success. Although the USSR gave its support to the Republican government there was no other official aid from other countries. However, a number of International Brigades and foreign volunteers did join forces with the Republicans.

The Spanish Civil War has often been seen as a prelude to the Second World War. Indeed there were a lot of tactics that were adopted that became widespread during WWII. For example, it was the first war where air power played a significant part and this included bombing of towns and other civilian targets. Armored vehicles were used in formation to drive the enemy back. Propaganda was also widely used against the Republican supporters which broke a lot of their resolve.

One of the main reasons General Franco and the Nationalists were victorious after three years of war was that the army was on their side. The Republicans did manage to train their own troops and they had become a good fighting force by the end of the conflict but it was not enough against the professional soldiers. There were some soldiers who defected from the army and went to fight for the Republicans but they were often suspected of being spies for the Nationalists and their expertise was not made use of. General Franco had taken all of the various Nationalist groups and unified them into a far stronger force than the Republicans. He also had far more support from other countries than the Nationalists did. Germany and Italy provided troops and equipment throughout the war.

Course and Practice of the Spanish Civil War

Click on the left image to access the PP given in class for notes - taken from Martin Blinkhorn's Lancaster Pamphlet on SCW....

Key Qs to review and answer in depth:

- What was the nature of the SCW?

- Why did the nationalists win?

- How did technology affect the outcome?

- What was the importance of foreign aid and      intervention?

- How did both sides gain support at home?

- TWE was this a revolution?

What was the key reason that the SCW result?

But how did the war affect lives of the Spanish caught up in the conflict, and those ordinary people who came to fight on the behalf of the Spanish Republic?  Nationalist soldiers and their allies were fully trained and battle hardened veterans.  The republican forces did include some professional soldiers, but also included a far greater percentage of militia, or part-time, fighters whose previous experience of battle was extremely limited.  What impact did these have on the war?  Did their guerilla tactics against a much better organised and equipped enemy have any impact on events?  How were their lives affected by their taking part?  Using the written and audio sources below, research the role of the Republican militia and their International Brigade allies....

The Abraham Lincoln Brigade Archives (ALBA) is a non-profit educational organization dedicated to promoting public awareness, research, and discussion about the Spanish Civil War and the American volunteers who risked their lives to fight fascism in Spain. Using its continually expanding archival collections in exhibitions, publications, performances, and educational programs, ALBA preserves the legacy of progressive activism and commitment of the Abraham Lincoln Brigade as an inspiration for present and future generations.

Inspired by the activism of the Abraham Lincoln Brigade, ALBA works toward a more widespread, profound, and nuanced awareness of the history of America’s progressive traditions among high school students, college students, scholars, and the public at large. We hope and intend that this awareness will allow progressive communities in the United States and elsewhere to develop effective strategies to meet the present and future challenges faced by the world, and to work more consciously and effectively toward a better and more just society.

Using the information in these two journal articles on the left, the BBC podcast below left + the interview below right, create a Powerpoint presentation detailing:

- What guerilla tactics are

- What guerrilla tactics were used in the SCW + by who?

- What other tactics were used in the SCW?

- At least 2 case studies of guerilla warfare

- What the guerrilla war achieved

- What the guerilla war failed to achieve

- What influence did the guerilla war have on the SCW?

- OPCVL your sources.....

Guernica - Picasso (1937) - What is the message of the painting? (annotate your paper version)

- complete your first answer to this question using only the source; watch the video by clicking on the painting; complete your second answer to this question; check your answer by clicking on the question mark in the bottom right corner....

Click for OPCVL link to youtube source on the left....

- what qs do you need to ask to understand the video clip??

Questions from source exercise w/13IB above.

OPCVL exercise based on these qs below....

Examples of student feedback about sourcework plenaries used over last few weeks of the year.

Fundamentally, students responded best to being presented with sources as a starter.  This allowed them to practice and develop their 'detective' skills to try and unravel their meanings.  Once attempted, the sources were left alone until the end of the lesson when the original conclusions or enquiries were revisited and reformulated.  This allowed the students very quickly to establish what they had learnt and also to keep continually developing the skills required when faced with a variety of history sources...

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